An electron emission device comprises an electron emission source for emitting electrons, and a display portion for displaying a picture when the emitted electrons collide with a fluorescent layer. One example of an electron emission display is a field emission display (FED). In a FED, electrons are emitted from an electron emitter provided on a cathode electrode, and the emitted electrons collide with a fluorescent layer provided on an anode electrode, so that the fluorescent layer emits light, thereby producing an image. In the FED, a triode structure comprising a cathode electrode, a gate electrode, and an anode electrode is widely used.
A good electron emission display requires sufficient brightness and a fine pitch. To achieve sufficient brightness, a sufficient emission current is required, and to achieve a fine pitch, an electron beam with a small diameter should be focused on the fluorescent layer. Therefore, various methods have been proposed to reduce the diameter of the electron beam emitted from the electron emission device.
By way of example, a structure comprising a focusing electrode which applies electric power between a cathode plate and an anode plate is disclosed in U.S. Pat. No. 5,508,584. FIG. 1 is a schematic sectional view illustrating a portion of a conventional electron emission display.
Referring to FIG. 1, a cathode plate 50 comprises a buffer layer 54 formed on a lower plate 52, a cathode electrode 56 formed on the buffer layer 54, and a micro-tip 60 formed within a gate hole 64 patterned on the cathode electrode 56. The gate hole 64 is employed for patterning a gate insulator 58 and a gate electrode 62 laminated in sequence.
Furthermore, an anode plate 48 comprises a transparent electrode 34 formed on a top plate 32, and a fluorescent layer 44 formed on the transparent electrode 34. Here, the fluorescent layer 44 corresponds to the micro-tip 60. A power supply (not shown) supplies electric power to the fluorescent layer 44.
Additionally, a focusing electrode 38 is provided for focusing the emitted electron beam and allowing the electrons to accurately collide with the fluorescent layer 44. The focusing electrode 38 is formed by patterning an insulator 36 and the electrode layer 34 in sequence, requiring an increased number of fabricating steps, thereby lowering productivity.
Furthermore, even though a focusing electrode 38 may be added to the electron emission display, the focusing of the electron beam is still generally unsatisfactory.